Designing UiO-66-Based Superprotonic Conductor with the Highest Metal–Organic Framework Based Proton Conductivity Subhabrata Mukhopadhyay Joyashish Debgupta Chandani Singh Rudraditya Sarkar Olivia Basu Samar K. Das 10.1021/acsami.9b01121.s001 https://acs.figshare.com/articles/journal_contribution/Designing_UiO-66-Based_Superprotonic_Conductor_with_the_Highest_Metal_Organic_Framework_Based_Proton_Conductivity/7926794 Metal–organic framework (MOF) based proton conductors have received immense importance recently. The present study endeavors to design two post synthetically modified UiO-66-based MOFs and examines the effects of their structural differences on their proton conductivity. UiO-66-NH<sub>2</sub> is modified by reaction with sultones to prepare two homologous compounds, that is, <b>PSM 1</b> and <b>PSM 2</b>, with SO<sub>3</sub>H functionalization in comparable extent (Zr:S = 2:1) in both. However, the pendant alkyl chain holding the −SO<sub>3</sub>H group is of different length. <b>PSM 2</b> has longer alkyl chain attachment than <b>PSM 1</b>. This difference in the length of side arms results in a huge difference in proton conductivity of the two compounds. <b>PSM 1</b> is observed to have the highest MOF-based proton conductivity (1.64 × 10<sup>–1</sup> S cm<sup>–1</sup>) at 80 °C, which is comparable to commercially available Nafion, while <b>PSM 2</b> shows significantly lower conductivity (4.6 × 10<sup>–3</sup> S cm<sup>–1</sup>). Again, the activation energy for proton conduction is one of the lowest among all MOF-based proton conductors in the case of <b>PSM 1</b>, while <b>PSM 2</b> requires larger activation energy (almost 3 times). This profound effect of variation of the chain length of the side arm by one carbon atom in the case of <b>PSM 1</b> and <b>PSM 2</b> was rather surprising and never documented before. This effect of the length of the side arm can be very useful to understand the proton conduction mechanism of MOF-based compounds and also to design better proton conductors. Besides, <b>PSM 1</b> showed proton conductivity as high as 1.64 × 10<sup>–1</sup> S cm<sup>–1</sup> at 80 °C, which is the highest reported value to date among all MOF-based systems. The lability of the −SO<sub>3</sub>H proton of the post synthetically modified UiO-66 MOFs has theoretically been determined by molecular electrostatic potential analysis and theoretical p<i>K</i><sub>a</sub> calculation of models of functional sites along with relevant NBO analyses. 2019-03-19 00:00:00 3 H proton UiO -66-based MOFs alkyl chain attachment proton conduction mechanism MOF-based proton conductors 3 H functionalization side arm 3 H group length pendant alkyl chain UiO -66 MOFs proton conductors NBO PSM 1 PSM 2 Designing UiO -66-Based Superprotonic Conductor proton conductivity side arms results UiO -66-NH 2 post synthetically activation energy